Governmental regulations regarding the use of volatile organic compounds (VOC) in industrial coatings and adhesives are becoming increasingly circumscribing with each passing year. Manufactures using adhesive compositions to bond various materials such as elastomeric materials to metal surfaces are therefore under an increasing pressure to reduce the amount of VOC utilized in their manufacturing processes. In order to continue utilizing adhesive and primer compositions based on organic solvents, these manufacturers will be required to purchase incineration equipment or reduce their manufacturing output in order to meet the increasingly demanding regulations. The purchase of incineration equipment and/or the reduction in manufacturing output will effectively reduce the profitability of numerous manufacturers which may result in the loss of jobs, thereby contributing to the current decline in the economy.
A more desirable response to the regulations regarding the use of VOC is the development of aqueous adhesive and primer compositions which would replace the current solvent-based adhesive and primer compositions utilized by manufacturers. With utilization of aqueous adhesive and primer compositions, the manufactures can continue their operations at the same rate and avoid the purchase of expensive incinerator equipment while simultaneously reducing worker exposure to the hazardous VOC.
Previous efforts to develop aqueous adhesive and primer compositions are manifested in various U.S. patents. For example, U.S. Pat. No. 4,167,500 describes an aqueous adhesive composition that contains a water dispersible novolak phenolic resin, a methylene donor such as an acetal homopolymer or acetal copolymer, and water. The phenolic resins described are primarily derived from resorcinol and alkylphenols such as p-nonylphenol although various other polyhydroxy phenols are mentioned, such as phloroglucinol and pyrogallol.
U.S. Pat. No. 4,988,753 describes an aqueous dispersion for bonding natural and synthetic elastomers to metallic and non-metallic substrates under vulcanizing conditions. The adhesive composition contains a mixture of chlorosulfonated polyethylene and vinyl chloride/vinylidene chloride/acrylic acid copolymer, an organic polynitroso compound, and a coreactive compound selected from diallyl acrylamide and phenylene bis-maleic acid imide. The adhesive composition may optionally contain other additives such as metal oxides, lead salts, and peroxides.
U.S. Pat. No. 5,036,122 describes an aqueous adhesive composition containing a latex of a polymerized conjugated diene, a poly-C-nitroso compound, and a polymaleimide compound which is a polymer of a bis-maleimide. The polymerized conjugated diene is preferably poly-2,3-dichlorobutadiene of poly-1,1,2-trichlorobutadiene. The adhesive may optionally contain additives such as carbon black, metallic oxides, and surfactants.
For purposes of further background, traditional adhesives utilized for bonding elastomeric materials to metal are frequently susceptible to the high temperature conditions experienced in the molding devices utilized in the bonding process. The molding devices which position and support the adhesive-coated metal parts are typically preheated or prebaked before the molten elastomeric material is applied to the metal part. This prebake frequently interferes with the bonding ability of the adhesive composition applied to the metal surface.
There is a continuing need for aqueous adhesive compositions which exhibit adhesion levels approximating the levels obtained by solvent-based adhesive compositions. Such aqueous adhesive compositions should be resistant to prebake conditions and provide for a flexible bond which is resistant to adverse environments such as corrosive materials and high temperature fluids.